Spool valves are used in a variety of applications to control fluid flow and fluid pressure in a system. Spool valves are typically disposed within a valve bore of a valve body and have one or more lands that are sized for sealing engagement with the valve bore. A spool valve is typically configured for reciprocal motion within the valve bore to control fluid flow among a plurality of ports in the valve body in fluid communication with the valve bore.
FIGS. 9 and 10 illustrate an exemplary prior art spool valve assemblies 900 and 1000. Exemplary assembly 900 is configured as a pressure regulator valve for use in an automobile transmission and exemplary assembly 1000 is configured as a torque converter pressure limit valve for use in an automobile transmission. As shown in FIG. 9, example prior art assembly 900 may include spool valve 902 slidably disposed within valve bore 904 of valve body 906. Spool valve 902 may have a plurality of lands 908a-e configured and dimensioned for sealing engagement with valve bore 904. Valve bore 904 may have a plurality of portions 909a-e that are configured and dimensioned for sealing engagement with corresponding ones of the plurality of lands 908a-e. Valve body 906 may also have a plurality of ports 910a-g in fluid communication with valve bore 904. Example assembly 900 may also include boost valve 912 disposed within boost sleeve 914 and spring 916 for resiliently biasing spool valve 902 to a normal position shown in FIG. 9. During use, a position of spool valve 902 within valve bore 904, which determines the direction of pressurized fluid flow among ports 910a-g, is determined by a balance of forces acting on the valve, including forces from pressurized fluid from one or more of ports 910a-g, a force from spring 916, and a force, if any, from boost valve 912. For example, port 910a includes a channel providing fluid communication between port 910d and land 908a. As pressure at port 910d increases, fluid pressure at port 910a and land 908a may begin to increase, eventually causing valve 902 to move to the right as viewed from the perspective of FIG. 9.
Exemplary assembly 1000 has similar components and functionality, and may include spool valve 1002 slidably disposed within valve bore 1004 of valve body 1006. In the illustrated example, valve bore 1004 may have a closed end 1005. Spool valve 1002 may have a plurality of lands 1008a-c configured and dimensioned for sealing engagement with valve bore 1004. Valve bore 1004 may have a plurality of portions 1009a-d that are configured and dimensioned for sealing engagement with corresponding ones of the plurality of lands 1008a-c. Valve body 1006 may also have a plurality of ports 1010a-e in fluid communication with valve bore 1004. Example assembly 1000 may also include plug 1012 secured by clip 1014 and spring 1016 for resiliently biasing spool valve 1002 in a leftward direction when viewed from the perspective shown in FIG. 10. In the illustrated example, ports 1010a and 1010d may be exhaust ports, and port 1010c may provide pressurized fluid to port 1010b when valve 1002 is in a normal position and land 1008b is not blocking port 1010b (position not illustrated). When pressurized fluid is passing from port 1010c to port 1010b, a portion of the fluid may pass through orifice 1018 and into port 1010e and act on faces of lands 1008a and 1008b. Because land 1008b has an outer diameter that is greater than an outer diameter of land 1008a, pressurized fluid from orifice 1018 acting on the two lands will create a pressure differential with a net force forcing valve 1002 in a rightward direction when viewed from the perspective shown in FIG. 10. When the fluid force from fluid passing through orifice 1018 becomes great enough to overcome the force of spring 1016, the valve will begin to move to the right, causing land 1008b to begin to close and eventually fully close port 1010b. In one example, exemplary assembly 1000 may be an automobile transmission torque converter pressure limit valve, port 1010c may provide fluid communication for “priority” pressure also sometimes referred to as “line” pressure to valve bore 1004, and port 1010b may provide fluid communication between the valve bore and a converter clutch circuit (“CCL”).
It can be common for fluid leakage to begin to occur in spool valve assemblies such as assemblies 900 and 1000, such as fluid leakage between one or more of the spool valve lands (e.g., one or more of lands 908a-e of assembly 900 or lands 1008a-c of assembly 1000) and adjacent valve bore portions (e.g., corresponding valve bore portions 909a-e of assembly 900 and 1009a-d of assembly 1000) due to excessive wear on one or more of the lands and valve bore portions. Such fluid leakage can alter the balance of forces acting the spool valve, e.g., valve 902 or valve 1002, resulting in the spool valve being in an improper location and not properly routing fluid among the associated valve bore ports, e.g., 910a-g or 1010a-e. Depending on the severity of the leakage and the type of valve, such leakage can have a variety of negative consequences, including damage to transmission components, causing the transmission to delay shifting or not shift at all, or otherwise cause drivability and longevity issues. For example, exemplary lands 908a (FIG. 9) and the combination of lands 1008a and 1008b (FIG. 10) are balance pressure lands that cooperate with other valve components to cause the associated spool valve 902, 1002 to move to the right as viewed from the perspective of FIGS. 9 and 10, and reduce fluid pressure in one or more of the fluid ports. If leakage begins to occur between balance land 908a or 1008a and 1008b and associated valve bore portion 909a, and 1009a, 1009b, the assembly 900, 1000 may not properly regulate fluid pressure, resulting in downstream transmission components receiving incorrect fluid pressure. Leakage at other ones of lands 908b-e or 1008b-c and associated valve bore portions may similarly cause the associated valve assembly to malfunction. To restore proper system operation, the malfunctioning spool valve assembly must be repaired or replaced.